1. Field of the Invention
Embodiments of the present invention relate to a sheet feeding mechanism and an image forming apparatus incorporating the sheet feeding mechanism.
2. Description of the Related Art
Some image forming apparatuses (e.g., copiers, printers, and facsimile machines) are designed to form a sheet conveyance path near a transfer roller so that the sheet conveyance path can be exposed to an outside of the apparatus for easily removing jammed paper(s) remaining near the transfer roller.
For example, Japanese Patent Application Publication Nos. 2011-085815 (JP-2011-085815-A), and 2004-020574 (JP-2004-020574-A) disclose configurations in which an openably retractable transfer cover unit is disposed on an outer surface of an image forming apparatus, and a transfer roller is disposed on an inner surface of the transfer cover unit. Similarly, Japanese Patent Application Publication No. 2000-231321 (JP-2000-231321-A) discloses a configuration in which not only a transfer roller but also one of a pair of timing rollers is disposed on an inner surface of such a transfer cover unit.
The transfer roller and the timing roller can be attached to the transfer cover unit, for example, by attaching respective rotatable axes of the rollers to the transfer cover unit fixedly as disclosed in Japanese Patent Application Publication No. 2000-231321 (JP-2000-231321-A) and swingably as disclosed in Japanese Patent Application Publication Nos. 2011-085815 (JP-2011-085815-A), 2004-020574 (JP-2004-020574-A), and 2006-030643 (JP-2006-030643-A). When the rotatable axes of the rollers are attached to the transfer cover unit fixedly, the transfer cover unit should be correctly positioned at at least four points (top, bottom, left, and right) by a projected and recessed engaging structure (e.g., main body positioning pins 38 and cover recessed portions 37 illustrated in FIG. 3 of JP-2000-231321-A). By contrast, when the rotatable axes of the rollers are attached to the transfer cover unit swingably, the transfer cover unit should have a rotation supporting mechanism (e.g., a receiving member 216, a support shaft member 218, and a compression spring 220 illustrated in FIG. 2 of JP-2011-085815-A).
As disclosed in JP-2011-085815-A, a main body of an image forming apparatus is made compact in size by narrowing a secondary transfer unit and a fixing unit located above the secondary transfer unit (refer to paragraph [0082] of JP-2011-085815-A). Therefore, a transit path of the secondary transfer unit is made different from a transit path of the transfer cover unit to temporarily lower the absolute height of the secondary transfer unit at opening and closing of the transfer cover unit, thereby avoiding interference with the fixing unit. Thereafter, the secondary transfer unit is lifted. (See FIGS. 6 and 9.)
To enable such a transit path, the secondary transfer unit is supported by a rotation supporting mechanism to the transfer cover unit. However, the secondary transfer unit cannot be part of the structure of the transfer cover unit due to the rotation supporting mechanism, and the rigidity of the transfer cover unit decreases. Further, the rotation supporting mechanism as disclosed in JP-2011-085815-A has a high degree of design freedom but a complicated configuration, and therefore a positioning mechanism for positioning the secondary transfer unit having a high degree of design freedom to the main body of the image forming apparatus should be located at at least four positions (top, bottom, left, and right) (a secondary transfer unit guide shaft 228 for a cutout 232 of a main body positioning member 230 and a cutout 238 of a secondary transfer unit positioning member 234 for a main body positioning boss 236 in FIG. 2).
In an image forming apparatus disclosed in JP-2004-020574-A, a linear guide member attached to a main body linearly guides a rotary shaft of a transfer roller attached to a transfer cover unit toward a drive roller attached to the main body. An opening at the leading edge of the linear guide member is located at a slightly lower position, and the transit path of the transfer roller becomes lower in the middle of opening and closing actions of the transfer cover unit but basically aligns with a transit path of the transfer cover unit. That is, the configuration of JP-2004-020574-A is not designed to avoid interference with parts provided in the main body, and therefore provides relatively less design freedom of space for a compact layout of the parts of the main body without interference with the transit path of the transfer roller.
In an image forming apparatus disclosed in JP-2000-231321-A, both the transfer roller and the timing roller can be exposed by opening the transfer cover unit, which can remove jammed paper in a vicinity of the rollers easily. Further, since the respective rotary shafts of the transfer roller and the pair or timing rollers are fixedly attached to the transfer cover unit, the above-described rotation supporting mechanism is not required. However, these transit paths of the rollers basically match the transit path of the transfer cover unit, and therefore the configuration of JP-2000-231321-A provides relatively less design freedom of space for a compact layout of the parts of the main body without interference with the transit path of the transfer roller.
Also in an image forming apparatus disclosed in JP-2006-030643-A, the transit paths of the transfer roller and the timing roller are basically the same as the transit paths of the transfer cover unit, and therefore the same issue regarding the interference with the parts of the main body (e.g., a photoconductive drums and an intermediate transfer belt) might arise when a compact layout of the image forming apparatus is attempted. Further, the mechanism of the image forming apparatus can be complicated due to arrangement of a transfer guide member and an operation lever to the transfer cover unit, which also leads to another issue regarding accuracy in positioning of the rotary shafts of the transfer roller and the timing roller.
Similar to JP-2011-085815-A, when a transfer roller and a timing roller are swingably disposed on the inner surface of the transfer cover unit, a simple mechanism or configuration to position the transfer roller and the timing roller with a drive roller and a timing roller provided in the main body is required.